1. General Troubleshooting Rules: When dealing with PLC system faults, follow the "One Touch, Two Look, Three Smell, Four Listen, Five Trace, Six Replace" method. - One Touch: Check the CPU temperature. It should not exceed 60°C. If it feels too hot, there might be an issue. - Two Look: Observe the status indicators on each board to see if they are functioning properly. - Three Smell: Detect any burnt odors that may indicate overheated components or cables. - Four Listen: Pay attention to unusual noises like loose screws or relay malfunctions. Also, listen to feedback from field staff. - Five Trace: Use the wiring diagrams and process flow charts to trace the fault location. - Six Replace: If uncertain, replace suspected parts to isolate the problem. 2. Specific Steps: When the PLC software is malfunctioning, first check if the CPU's RUN status is normal. If not, reset the CPU and re-download the control program. For hardware issues, follow this order: - First, check the power supply. Ensure the voltage is within ±5% of +24V. If the input is good but the output isn’t, replace the module. If the input is bad, check the transformer and possibly replace it. - If no power is detected, use the schematic, layout, and wiring diagrams to verify all connections. Check the circuit breaker with a multimeter. If the power is insufficient or overloaded, resolve the external issue before proceeding. - Understand the CPU operating mode (STOP, HOLDUP, STARTUP, RUN). If the CPU is in STOP or hold mode, re-upload the program. If the CPU is faulty, replace it with a compatible one. 3. Communication and Module Checks: Inspect communication cables and LED indicators for signs of failure. For digital output modules, each point acts like a standard switch. When online, test each point by checking the signal. If the signal is not present, the point may be faulty. Reconnect the wiring or replace the module. For digital input modules, when the coil is energized, the contact should close. If the test shows a break, check the wiring or update the software configuration. Analog modules function similarly, with each channel acting like a closed switch. If the state is off, the channel is faulty. Replace the module and adjust the address accordingly. 4. Power Module Considerations: During normal operation, avoid cutting power to output modules. This could cause relays to become open, leading to errors. To test, coordinate with on-site operators to manually operate the equipment before removing the power line. 5. Switch Testing: Test various switches such as relays, proximity switches, and air switches. Based on their normally open or closed state, compare with known good devices. If the state is opposite, the device is likely faulty. 6. Communication Module Test: Use a known working communication module to test the current one. If the new module works, the original one is likely defective. 7. Wire Testing: Test wires using an on-off method. Connect a known good wire to an unknown one and measure the continuity. This helps identify faulty cables. 8. Resistance Testing: Measure resistance when the system is not powered. When the battery is active, check the voltage. Most issues can be resolved through these methods. Always prioritize safety, especially when working with AC 220V and DC 24V systems. Follow all electrical and gas safety procedures to ensure safe operations.
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